A carbon nitride-based photocatalyst capable of adapting to complex water environment, a preparation method thereof and application of the photocatalyst in photocatalytic production of H2O2

Abstract

The application discloses a carbon nitride-based photocatalyst suitable for complex water environment and a preparation method and application of the photocatalyst in photocatalytic H2O2 production. The application belongs to the field of photocatalysis. The application aims to solve the technical problem of high production cost and narrow application range of the existing photocatalytic H2O2 production method which depends on organic sacrificial agent, pure O2 and deionized water. The photocatalyst is composed of carbon nitride nanosheets and Ni-Ag nanoparticles uniformly loaded on the surface of the nanosheets. The method comprises the following steps: mixing a water dispersion of carbon nitride nanosheets with a Ni(NO3)2.6H2O solution and an AgNO3 solution, stirring and reacting in the dark, then adding a NaBH4 solution drop by drop, continuously stirring and reacting in the dark, centrifuging, washing and drying to obtain the carbon nitride-based photocatalyst. The photocatalyst prepared by the application exhibits excellent catalytic performance in deionized water or tap water without adding an organic sacrificial agent and without additionally introducing O2. The photocatalyst is used for photocatalytic water H2O2 production.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of photocatalysis, and particularly relates to a carbon nitride-based photocatalyst capable of adapting to complex water environments, a preparation method thereof and application of the photocatalyst in photocatalytic H2O2 production. BACKGROUND

[0002] As a byproduct, H2O2 is an oxidant with only O2 and H2O, and is more commonly used in chemical synthesis, wastewater treatment, medical sterilization and other fields. However, the anthraquinone method commonly used in industry for synthesizing H2O2 consumes a large amount of energy, causes serious environmental pollution, and is prone to cause explosions. Compared with the anthraquinone method, photocatalytic synthesis of H2O2 only needs O2, H2O, sunlight and a semiconductor catalyst, and is safer and more environmentally friendly, so it has gradually attracted the attention of researchers. At present, most of the research can only achieve high H2O2 yield in deionized water with the addition of an organic sacrificial agent and the additional introduction of pure O2. The addition of the organic sacrificial agent (isopropyl alcohol, ethanol, etc.) will also cause the generation of ketone or aldehyde substances in the photocatalytic process, which will adversely affect the subsequent separation and purification of H2O2. At the same time, if the newly generated ketone or aldehyde and the remaining organic alcohol substances are not properly treated, they will also cause environmental pollution. In addition, the dependence on pure water and pure O2 will not only increase the cost of photocatalytic synthesis of H2O2, but also greatly reduce its practicability.

[0003] At present, although there are many studies on photocatalytic oxygen reduction for synthesizing H2O2, it is still a difficult problem to design a catalyst that does not depend on an organic sacrificial agent, pure O2 and deionized water. SUMMARY

[0004] The purpose of the present application is to solve the technical problem of high production cost and narrow application range caused by the dependence of the existing method for photocatalytic H2O2 production on an organic sacrificial agent, pure O2 and deionized water, and to provide a carbon nitride-based photocatalyst capable of adapting to complex water environments, a preparation method thereof and application of the photocatalyst in photocatalytic H2O2 production.

[0005] The technical solution of the present application is as follows:

[0006] One of the purposes of the present application is to provide a carbon nitride-based photocatalyst capable of adapting to complex water environments, which is composed of carbon nitride nanosheets and Ni-Ag composite nanoparticles uniformly loaded on the surface of the nanosheets.

[0007] Further limited, the thickness of the carbon nitride nanosheet is 20-30 nm, the particle size of the Ni-Ag composite nanoparticle is 30-40 nm, the loading amount of the Ni-Ag composite nanoparticle is 2.5-5.5% of the mass of the carbon nitride nanosheet, and the mass ratio of Ni to Ag is (2-4):0.9.

[0008] The second object of the present application is to provide a preparation method of carbon nitride-based photocatalyst capable of adapting to complex water environment, which is carried out according to the following steps:

[0009] The water dispersion of carbon nitride nanosheets is mixed with a Ni(NO3)2·6H2O solution and an AgNO3 solution, and then stirred and reacted in the dark, followed by dropwise addition of a NaBH4 solution, and continuous stirring and reaction in the dark, centrifugation, washing and drying to obtain CNNS / Ni-Ag, i.e., the carbon nitride-based photocatalyst.

[0010] Further limitation, the preparation process of carbon nitride nanosheets: made from urea by twice calcination.

[0011] Further limitation, the temperature of twice calcination is 450-600 DEG C, the heating rate is 4-6 DEG C / min, the time is 2-4h, and water washing and drying are carried out between the two times of calcination.

[0012] Further limitation, the concentration of the water dispersion of carbon nitride nanosheets is 4-6g / L.

[0013] Further limitation, the concentration of the Ni(NO3)2·6H2O solution is 20-40g / L, and the concentration of the AgNO3 solution is 4-16g / L.

[0014] Further limitation, the stirring and reaction in the dark is carried out for 1.5-2.5h.

[0015] Further limitation, the mass ratio of NaBH4 to carbon nitride nanosheets is (0.2-0.4):1, and the concentration of the NaBH4 solution is 10-14g / L.

[0016] Further limitation, the continuous stirring and reaction in the dark is carried out for 3-5h.

[0017] The third object of the present application is to provide an application of carbon nitride-based photocatalyst capable of adapting to complex water environment in photocatalytic production of H2O2.

[0018] The fourth object of the present application is to provide a method for photocatalytic production of H2O2 with high efficiency, which is carried out according to the following steps:

[0019] The above-mentioned carbon nitride-based photocatalyst is added to water, and then stirred in the dark, followed by photocatalytic reaction at room temperature.

[0020] Further limitation, the water is tap water.

[0021] Further limitation, the dosage of the carbon nitride-based photocatalyst is 0.5-1.5g / L.

[0022] Further limitation, the stirring in the dark is carried out for 10-30min.

[0023] Compared with the prior art, the present application has the following advantages:

[0024] (1) The CNNS / Ni-Ag provided by the application realizes the preparation process of high-efficiency photocatalytic oxygen reduction to generate H2O2 in deionized water without adding an organic sacrificial agent and without additional pure O2. The H2O2 yield is as high as 681.2 μmol / L / h, and the material has good cycle stability.

[0025] (2) The CNNS / Ni-Ag prepared by the application has a photocatalytic oxygen reduction efficiency of 446.3 μmol / L / h to generate H2O2 in a complex water environment (such as tap water) without any treatment, has low environmental requirements, exhibits high practicability, and has a wider application range.

[0026] (3) The method for synthesizing CNNS / Ni-Ag provided by the application has simple operation and simple required equipment, and the reaction conditions are relatively mild. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 SEM image of the CNNS / Ni-Ag photocatalyst prepared in Example 1;

[0028] Figure 2 TEM image of the CNNS / Ni-Ag photocatalyst prepared in Example 1; wherein (a) is TEM, and (b) is HRTEM;

[0029] Figure 3 XPS test results of the CNNS / Ni-Ag photocatalyst prepared in Example 1; wherein (a) is -C1s, (b) is -N1s, (c) is -Ni2p, and (d) is -Ag3d;

[0030] Figure 4 O2 adsorption energy calculation results of the CNNS, the catalysts of Comparative Examples 1-2, and Example 1; (a) is adsorption energy, and (b) is an adsorption model schematic diagram;

[0031] Figure 5 Performance diagram of the CNNS / Ni-Ag prepared in Example 1 for photocatalytic synthesis of H2O2 in deionized water and tap water;

[0032] Figure 6 Stability test results of the CNNS / Ni-Ag prepared in Example 1 for photocatalytic production of H2O2 in deionized water without a sacrificial agent and without additional O2. DETAILED DESCRIPTION

[0033] In order to make the objects, technical solutions and advantages of the application clearer, the following further describes the application in combination with examples. It should be understood that the specific examples described herein are only used to explain the application, and are not used to limit the application.

[0034] The experimental procedures used in the following examples are conventional unless otherwise specified. The materials, reagents, methods and instruments used are conventional unless otherwise specified and are available to those skilled in the art through commercial channels.

[0035] The terms "comprising," "including," "having," "containing," or any other similar word, as used herein, are intended to encompass non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that comprises a list of elements is not necessarily limited to those elements but can include other elements not expressly listed or inherent to such composition, step, method, article, or apparatus.

[0036] When expressing a range, a preferred range, or a range defined by a series of upper preferred values and lower preferred values for an equivalent, concentration, or other value or parameter, it is to be understood that all ranges formed by any pair of an upper or preferred value from any range and a lower or preferred value from any range, whether or not the range is expressly disclosed, are specifically disclosed. For example, where a range "1 to 5" is disclosed, the described range is to be construed as including the range "1 to 4," "1 to 3," "1 to 2," "1 to 2 and 4 to 5," "1 to 3 and 5," etc. When numerical ranges are described herein, unless the context indicates otherwise, the range is intended to include the end values and all the integers and fractions within that range. In the application specification and claims, range definitions can be combined and / or interchanged, unless otherwise indicated, and these ranges include all sub-ranges contained therein.

[0037] The indefinite articles "a" and "an," as used herein in the specification, unless clearly indicated to the contrary, should be understood to mean one or at least one. The use of "or" in the context of "A / B or C" means any of the following: A, B, or C; A / B, and C; A / B; B / C; A and B but not C; A and C but not B; B and C but not A; etc. The use of "and" in the context of "A and / or B" means any of the following: A, B, or both A and B.

[0038] As used herein, the singular form "a", "an" and "the" include plural references unless the context clearly dictates otherwise. As used herein, the term "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation of the application. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily all referring to a single, alternative embodiment, or a single group of alternative embodiments.

[0039] The endpoints of the ranges and any values or parameters within such ranges are not limited to the precise values stated. Such ranges are intended to cover values which are approximately the same as those ends. Numerical ranges include all values from and including the lower and the upper values, in increments of one unit provided that there is a context for the use of such a value. For example, if the context indicates that only a subset of the numerical range is intended, only the integer values within that subset are intended to be within the scope of the disclosure. The endpoints of the ranges can be combined with other ranges or points to form new ranges. These new ranges are also within the scope of the disclosure.

[0040] The preparation method of the carbon nitride-based photocatalyst capable of adapting to complex water environment of the embodiment is carried out according to the following steps:

[0041] (1) 12 g of urea was weighed in a covered crucible, and was heated to 550°C at a rate of 5°C / min in a muffle furnace and was kept at 550°C for 4 h. The obtained product was washed with deionized water for five times and was dried, and then was repeatedly placed in a crucible, heated to 500°C at a rate of 5°C / min in a muffle furnace and was kept at 500°C for 2 h to obtain carbon nitride nanosheets.

[0042] (2) 0.2 g of the carbon nitride nanosheets was ultrasonically dispersed in 40 mL of deionized water, and was continuously stirred for 30 min to be uniformly dispersed to obtain a carbon nitride nanosheet water dispersion. 600.8 mg of Ni(NO3)2·6H2O and 189.4 mg of AgNO3 were weighed and dissolved in 20 mL of deionized water respectively to obtain a Ni(NO3)2·6H2O solution and an AgNO3 solution respectively.

[0043] (3) 1 mL of the Ni(NO3)2·6H2O solution and 0.3 mL of the AgNO3 solution were added to the carbon nitride nanosheet water dispersion obtained in step (2), and was stirred in the dark for 2 h. Then 5 mL of a NaBH4 solution with a concentration of 12 g / L was added dropwise to the above mixture, and was continuously stirred in the dark for 4 h. After centrifugation, deionized water washing and vacuum drying, the obtained product was recorded as CNNS / Ni-Ag.

[0044] Figure 1 It is a SEM image of the CNNS / Ni-Ag photocatalyst of Example 1. On the surface of CNNS, Ni-Ag nanoparticles with a size of 30-40 nm can be obviously observed.

[0045] Figure 2 It is a TEM and HRTEM test result of the CNNS / Ni-Ag photocatalyst of Example 1. The TEM image of CNNS / 3Ni-0.9Ag shows that the CNNS surface is loaded with nanoparticles with a size of 30-40 nm. From the HRTEM image of the composite material, it can be seen that the nanoparticles have lattice fringes with a spacing of 0.202 nm and 0.240 nm, which correspond to the (111) crystal planes of metallic Ni and Ag respectively, indicating that the two metals are successfully loaded on the surface of CNNS and form composite nanoparticles in contact with each other.

[0046] Figure 3XPS test results of CNNS / Ni-Ag photocatalyst of Example 1. Two peaks at 284.83 eV and 288.23 eV in the C 1s spectrum of CNNS correspond to -C-C, -C-N3 in carbon nitride. It can be seen from the N 1s spectrum that the peaks at 398.45 eV, 399.37 eV and 400.98 eV are respectively attributed to C-N=C, N-C3 and -NH in carbon nitride x . The peaks at 852.47 eV and 869.1 eV in the Ni 2p spectrum of CNNS / 3Ni are 2p 0 and 2p 3 / 2 of Ni 1 / 2 , indicating that elemental Ni is deposited on the surface of the material. In addition, the Ni 2p spectrum also shows the peaks of 2p 2+ (857.2 eV) and 2p 3 / 2 (873.48 eV) of Ni 1 / 2 , and there are corresponding satellite peaks at higher binding energy, which may be caused by partial oxidation of Ni due to too long time of the composite material in air. The Ag 3d spectrum shows characteristic peaks corresponding to Ag 0 3d 3 / 2 (366.85 eV) and Ag 0 3d 5 / 2 (373.14 eV).

[0047] Comparative Example 1: The difference between this comparative example and Example 1 is that in step (3), 1 mL of Ni(NO3)2 solution with a concentration of 30.04 g / L is added to the carbon nitride nanosheet aqueous dispersion obtained in step (2). A carbon nitride-based photocatalyst loaded with only Ni nanoparticles is obtained, which is denoted as CNNS / Ni.

[0048] Comparative Example 2: The difference between this comparative example and Example 1 is that in step (3), 0.3 mL of Ag(NO3)2 solution with a concentration of 9.47 g / L is added to the carbon nitride nanosheet aqueous dispersion obtained in step (2). A carbon nitride-based photocatalyst loaded with only Ag nanoparticles is obtained, which is denoted as CNNS / Ag.

[0049] DFT calculation was performed on the catalysts obtained in Example 1 and Comparative Examples 1-2. It can be seen from Table 1 that the loading of Ni, Ag and Ni-Ag can all reduce the adsorption energy of O2 on the surface of the material. Among them, the adsorption energy of O2 on the surface of CNNS / Ni-Ag is the most negative due to the loading of Ni-Ag composite nanoparticles, indicating that the adsorption of O2 molecules on the surface of CNNS / Ni-Ag is easier to proceed. In addition, the O-O bond length of O2 molecules on the surface of CNNS / Ni-Ag is the longest, indicating that O2 molecules are more easily activated. These can prove that the CNNS / Ni-Ag photocatalyst can efficiently produce H2O2 under different O2 conditions. Figure 4 ​

[0050] Application Example 1: The method for photocatalytic synthesis of H2O2 is as follows:

[0051] (1) 50 mg of CNNS / Ni-Ag catalyst prepared in Example 1 was ultrasonically dispersed in 50 mL of tap water, and stirred in the dark for 20 min to allow H2O and O2 originally dissolved therein to reach adsorption-desorption equilibrium on the surface of the material.

[0052] (2) Subsequently, the mixture was moved to a photocatalytic reactor and placed under a 300 W xenon lamp for photocatalytic reaction at room temperature.

[0053] Comparative Application Example 1: Deionized water without any influencing factors was used as a control group.

[0054] The yield of H2O2 was determined by iodometric method: 1.5 mol / L potassium hydrogen phthalate solution and 1.5 mol / L potassium iodide solution were mixed (1.5 mL each), and then the solution after photocatalytic reaction for different times and filtration of the catalyst was color-developed for 10 min. Finally, the absorbance of the color-developed solution at 350 nm was determined by spectrophotometry, and the yield of H2O2 was obtained by combining the corresponding standard curve.

[0055] The results are shown in Table 1. Figure 5 As can be seen, in deionized water and tap water, the H2O2 yield reached 681.2 μmol g -1 h -1 and 436.4 μmol g -1 h -1 , respectively. The results show that the photocatalyst of the present application can exhibit good photocatalytic H2O2 activity in untreated tap water, indicating that it has high practical value.

[0056] Figure 6 The results of the stability test of the CNNS / Ni-Ag composite material obtained in Example 1 for photocatalytic production of H2O2 in deionized water without a sacrificial agent and without additional O2 are shown in Table 2. The results show that after repeated use for five times, the photocatalytic H2O2 production efficiency of CNNS / Ni-Ag decreased from the initial 681.2 μmol L -1 h -1 to 630.4 μmol L -1 h -1 , with a performance decay of less than 8%, indicating that the material has high stability.

[0057] The above merely describes preferred specific embodiments of the present application, which are based on different implementations of the overall concept of the present application, and the protection scope of the present application is not limited thereto. Any changes or replacements that are easily conceived by those skilled in the art within the technical scope disclosed by the present application shall be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for photocatalytic water to produce H2O2 efficiently, characterized in that, The carbon nitride-based photocatalyst is added into water, stirred in dark, and then photocatalytic reaction is carried out at room temperature; The carbon nitride-based photocatalyst is composed of carbon nitride nanosheets and Ni-Ag composite nanoparticles uniformly loaded on the surface of the nanosheets, wherein the metal elements Ni and Ag form composite nanoparticles in contact with each other; The thickness of the carbon nitride nanosheets is 20-30 nm, the particle size of the Ni-Ag composite nanoparticles is 30-40 nm, the loading amount of the Ni-Ag composite nanoparticles is 2.5-5.5% of the mass of the carbon nitride nanosheets, and the mass ratio of Ni to Ag is (2-4):0.

9.

2. The method of photocatalytic water to efficiently produce H2O2 according to claim 1, characterized in that, The preparation method of the carbon nitride-based photocatalyst: The water dispersion of the carbon nitride nanosheets is mixed with a solution of Ni(NO3)2·6H2O and a solution of AgNO3, and stirred in dark for reaction, then a solution of NaBH4 is added drop by drop, and the stirring in dark for reaction is continued, followed by centrifugation, washing, and drying to obtain CNNS / Ni-Ag, i.e. the carbon nitride-based photocatalyst.

3. The method of photocatalytic water to efficiently produce H2O2 according to claim 2, characterized in that, The preparation process of the carbon nitride nanosheets: prepared from urea through two times of calcination.

4. The method of photocatalytic water to efficiently produce H2O2 according to claim 3, characterized in that, The temperature of the two times of calcination is 450-600℃, the heating rate is 4-6℃ / min, and the time is 2-4h, and water washing and drying are carried out between the two times of calcination.

5. The method of photocatalytic water to efficiently produce H2O2 according to claim 2, characterized in that, The concentration of the water dispersion of the carbon nitride nanosheets is 4-6g / L, the concentration of the solution of Ni(NO3)2·6H2O is 20-40g / L, and the concentration of the solution of AgNO3 is 4-16g / L, and the stirring in dark for reaction is 1.5-2.5h.

6. The method of photocatalytic water to efficiently produce H2O2 according to claim 2, characterized in that, The mass ratio of NaBH4 to the carbon nitride nanosheets is (0.2-0.4):1, the concentration of the solution of NaBH4 is 10-14g / L, and the stirring in dark for reaction is continued for 3-5h.

7. The method of photocatalytic water-efficient H2O2 production according to claim 1, characterized by, The water is tap water, the dosage of the carbon nitride-based photocatalyst is 0.5-1.5g / L, and the stirring in dark is 10-30min.

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